The present invention relates to a system for assisting in regenerating depollution means associated with means forming an oxidation catalyst integrated in an exhaust line of a diesel-engine motor vehicle.
More particularly, the invention relates to a system in which the engine is associated with means comprising a common manifold for feeding fuel to the cylinders of the engine and adapted, at constant torque, to implement a strategy of regeneration by injecting fuel in to the cylinders using at least one post-injection.
While depollution means, e.g. a particle filter, are being regenerated, periods during which the driver's foot on the vehicle accelerator is lifted (no fuel injection in normal operation), and periods of engine idling (exhaust temperature very low) are problematic since they cause a drop in the temperature of the exhaust, i.e. of the exhaust line and the elements included therein.
The use of one of more post-injections during these periods in the life of the engine enables the temperature drop of the exhaust line to be limited, by relying on the catalytic conversion of the hydrocarbons (HCs) produced by combustion of the poet-injection(s) into the engine.
Nevertheless, those strategies rely on the catalyst-forming means operation exothermally, where said means are considered as being activated and comprise, for example, an oxidation catalyst or a NOx trap with a CO/HC oxidation function.
During periods while the engine is returning to idling, after the foot on the accelerator has been raised, there is not main injection nor any pilot injection, so the or each post-injection does not burn in the cylinder since it does no more than vaporize fuel in the form of HCs for conversion by the catalyst-forming means.
The inlet temperature at the oxidation catalyst-forming means is thus very low in spite of the exothermal nature of the catalytic combustion of the HCs delivered by the or each post-injection, so the front face of the catalyst-forming means cool down progressively and its conversion activity runs down progressively.
While the engine is idling, and in spite of using one or more post-injections, the temperature that the inlet to the catalyst-forming means is relatively low. The strategy of post-injection while idling also relies on catalytic conversion of the HCs produced by the combustion of the post-injection(s) into the engine. In spite of this catalytic exothermic reaction, the front face of the catalyst-forming means cools down progressively and its conversion activity runs down progressively.
During a prolonged period of idling, it can happen that the catalyst-forming means are thus no longer sufficiently active to convert all of the HCs, which leads to HC peaks downstream from the catalyst-forming means, and even to blue fumes and/or exhaust odors.
Furthermore, the use of post-injections leads to fuel diluting the lubricating oil, thereby degrading its lubricating properties, and in particular reducing its viscosity, which can lead to engine damage if the viscosity becomes too low.